The present invention relates to a slip control system that brings relative rotation, i.e., slip rotation between input and output elements of a torque converter used in an automatic transmission closer to a desired value, and particularly to techniques for slip control during a transition from a non-slip-control area to a slip-control area.
In recent years, there have been proposed and developed various slip control systems that perform slip control for a torque converter lock-up clutch. A pre-compensator equipped slip control system has been disclosed in Japanese Patent Provisional Publication No. 2000-145948 (hereinafter is referred to as xe2x80x9cJP2000-145948xe2x80x9d). In the slip control system disclosed in JP2000-145948, instead of directly using a value of target slip rotation (hereinafter is referred to as a xe2x80x9ctarget slip rotation xcfx89SLPTxe2x80x9d indicated in terms of an angular velocity), a compensated value of target slip rotation (hereinafter is referred to as a xe2x80x9ccompensated target slip rotation xcfx89SLPTCxe2x80x9d) produced by passing target slip rotation xcfx89SLPT through the pre-compensator is used for slip control. The pre-compensator functions to determine the transient response of the slip control system singly. Slip control is executed so that a value of actual slip rotation (hereinafter is referred to as an xe2x80x9cactual slip rotation xcfx89SLPRxe2x80x9d) is brought closer to the compensated target slip rotation xcfx89SLPTC filtered or compensated for by means of the pre-compensator. In the system of JP2000-145948, when the torque converter is shifted from the non-slip-control area to the slip-control area, target slip rotation xcfx89SLPT is switched from actual slip rotation xcfx89SLPR to a value of required slip rotation (hereinafter is referred to as a xe2x80x9crequired slip rotation xcfx89SLPT0xe2x80x9d) based on both a rotational speed of a turbine runner and a throttle opening, and the required slip rotation xcfx89SLPT0 passes through the pre-compensator to produce compensated target slip rotation xcfx89SLPTC, and thus actual slip rotation xcfx89SLPR is feedback-controlled closer to compensated target slip rotation xcfx89SLPTC based on required slip rotation xcfx89SLPT0. Therefore, even when shifting from the non-slip-control area to the slip-control area, it is possible to provide a designated transient-response characteristic determined by the pre-compensator, thereby reducing shocks during engagement of the torque converter lock-up clutch.
In the system of JP2000-145948, arithmetic calculation for compensated target slip rotation xcfx89SLPTC (corresponding to the transient response), is executed by the pre-compensator immediately when shifting from the non-slip-control area to the slip-control area. On the other hand, an engagement pressure of the lock-up clutch tends to rise with a delay in the response from the time when shifting to the slip-control area. During a period of time that the engagement pressure of the lock-up clutch is still low and thus it is impossible to satisfactorily engage the lock-up clutch, the actual slip rotation cannot be changed. As a result, actual slip rotation xcfx89SLPR tends to decrease with a response delay from the time when shifting to the slip-control area. During such a time period, compensated target slip rotation xcfx89SLPTC (corresponding to the transient response) is gradually decreasing, and therefore a deviation or a difference between actual slip rotation xcfx89SLPR and compensated target slip rotation SLPTC tends to increase. That is, the follow-up performance of actual slip rotation xcfx89SLPR toward compensated target slip rotation xcfx89SLPTC is deteriorated. Control constants for the pre-compensator are preset or preprogrammed so that the transient response is optimized when target slip rotation xcfx89SLPT is changing in the slip-control area. However, the value of actual slip rotation xcfx89SLPR occurring at the beginning of shifting to the slip-control area tends to be considerably higher than the value of target slip rotation xcfx89SLPT computed in the slip-control area. In other words, there is a great deviation between actual slip rotation xcfx89SLPR occurring at the beginning of shifting to the slip-control area and target slip rotation xcfx89SLPT computed in the slip-control area. Thus, it is difficult to provide an optimal transient performance by computing the transient response (compensated target slip rotation xcfx89SLPTC) by means of the pre-compensator during shifting to the slip-control area (including initial stages of shifting to the slip-control area) from the transient response characteristic preprogrammed to be suitable to the time when target slip rotation xcfx89SLPT is changing in the slip-control area. In a similar manner, in a feed-back control system arranged at the back of the pre-compensator, assuming that control constants or control gains for the feed-back control system are preset or preprogrammed to be suitable to the time when target slip rotation xcfx89SLPT is changing in the slip-control area, there is a possibility that an optimal response of the feed-back control system cannot be obtained during shifting to the slip-control area. In case of the slip control for the torque converter, the system control responsiveness obtained during a period of time in which actual slip rotation xcfx89SLPR is converging to target slip rotation xcfx89SLPT, exerts a great influence upon the driver""s feeling. In particular, if the slip rotation becomes excessively small and thus the torque converter lock-up clutch temporarily shifts to its fully engaged state, undesirable shocks occur. To enhance the transient performance during the transition from the non-slip-control area to the slip-control area, a pre-compensator suitable to the transient response during the transition from the non-slip-control area to the slip-control area can be further added, or control constants suitable for during the transition from the non-slip-control area to the slip-control area can be preprogrammed in addition to the control constants suitable for the time when target slip rotation xcfx89SLPT is changing in the slip-control area. In such a case, the control logic of the control system is very troublesome.
Accordingly, it is an object of the invention to provide a pre-compensator equipped slip control system for a torque converter, which avoids the aforementioned disadvantages.
It is another object of the invention to provide a pre-compensator equipped slip control system for a torque converter which is capable of improving the follow-up performance of actual slip rotation xcfx89SLPR toward compensated target slip rotation xcfx89SLPTC filtered or compensated for by means of the pre-compensator without complicating the control logic.
In order to accomplish the aforementioned and other objects of the present invention, a slip control system for a torque converter employing a lock-up clutch, comprises a pre-compensator that determines a follow-up characteristic of an actual value of a controlled quantity to a desired value of slip rotation between input and output elements of the torque converter and makes a filtering process to a target slip rotation corresponding to the desired value of slip rotation to produce a compensated target slip rotation, a feedforward control section that determines a lock-up clutch engagement pressure by way of feedforward control during a period of time from a time when the torque converter is shifted from a torque-converter action area to a slip-control area to a time when an actual slip rotation corresponding to the actual value of the controlled quantity becomes less than a predetermined slip-rotation threshold value, a feedback control section that controls the lock-up clutch engagement pressure by way of feedback control from the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area, so that the actual slip rotation is brought closer to the compensated target slip rotation, the pre-compensator being initialized by the actual slip rotation at the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area, and a target slip rotation switching section that switches the target slip rotation from the actual slip rotation to a required slip rotation based on engine and vehicle operating conditions at the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area.
According to another aspect of the invention, a slip control system for a torque converter employing a lock-up clutch, comprises a pre-compensating means for determining a follow-up characteristic of an actual value of a controlled quantity to a desired value of slip rotation between input and output elements of the torque converter and for making a filtering process to a target slip rotation corresponding to the desired value of slip rotation to produce a compensated target slip rotation, a feedforward control means for determining a lock-up clutch engagement pressure by way of feedforward control during a period of time from a time when the torque converter is shifted from a torque-converter action area to a slip-control area to a time when an actual slip rotation corresponding to the actual value of the controlled quantity becomes less than a predetermined slip-rotation threshold value, a feedback control means for controlling the lock-up clutch engagement pressure by way of feedback control from the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area, so that the actual slip rotation is brought closer to the compensated target slip rotation, the pre-compensating means being initialized by the actual slip rotation at the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area, and a target slip rotation switching means for switching the target slip rotation from the actual slip rotation to a required slip rotation based on engine and vehicle operating conditions at the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area.
According to a further aspect of the invention, a method for controlling slip rotation between input and output elements of a torque converter employing a lock-up clutch, the method comprises determining a filter constant by which a transient response is determined, pre-compensating a target slip rotation corresponding to a desired value of slip rotation at the filter constant by way of a pre-compensator to produce a compensated target slip rotation, feedforward-controlling a lock-up clutch engagement pressure during a period of time from a time when the torque converter is shifted from a torque-converter action area to a slip-control area to a time when an actual slip rotation corresponding to an actual value of a controlled quantity becomes less than a predetermined slip-rotation threshold value, feedback-controlling the lock-up clutch engagement pressure from the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area, so that the actual slip rotation is brought closer to the compensated target slip rotation, initializing the pre-compensator by the actual slip rotation at the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area, and switching the target slip rotation from the actual slip rotation to a required slip rotation based on engine and vehicle operating conditions at the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area.
According to a still further aspect of the invention, a method for controlling slip rotation between input and output elements of a torque converter employing a lock-up clutch, the method comprises determining, based on a throttle opening and a transmission output speed, whether the torque converter is in a torque-converter action area, in a slip-control area, or in a lock-up engagement area, calculating a required slip rotation based on the throttle opening and a turbine speed, calculating an actual slip rotation as a difference between a pump-impeller speed and the turbine speed, determining a filter constant by which a transient response is determined, pre-compensating a target slip rotation corresponding to a desired value of slip rotation at the filter constant by way of a pre-compensator to produce a compensated target slip rotation, switching the target slip rotation from the actual slip rotation to the required slip rotation at the time when the actual slip rotation becomes less than a predetermined slip-rotation threshold value after shifting from the torque-converter action area to the slip-control area, feedforward-controlling a lock-up clutch engagement pressure during a period of time from a time when the torque converter is shifted from the torque-converter action area to the slip-control area to a time when the actual slip rotation corresponding to an actual value of a controlled quantity becomes less than the predetermined slip-rotation threshold value, feedback-controlling the lock-up clutch engagement pressure from the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area, so that the actual slip rotation is brought closer to the compensated target slip rotation, and initializing the pre-compensator by the actual slip rotation at the time when the actual slip rotation becomes less than the predetermined slip-rotation threshold value after shifting to the slip-control area.
According to another aspect of the invention, a slip control system for a torque converter employing a lock-up clutch comprises a slip-control area section that determines whether the torque converter is in a torque-converter action area or in a slip-control area according to a throttle opening and a vehicle speed, a feedforward control section that determines a lock-up clutch engagement pressure by way of feedforward control for a predetermined period when the torque converter is shifted from the torque-converter action area to the slip-control area, a required slip rotation calculation section that calculates a required slip rotation between input and output elements of the torque converter based on engine operating conditions, a pre-compensator that determines a controlled transient characteristic of an actual slip rotation to the required slip rotation and makes a compensated target slip rotation corresponding to the controlled transient characteristic after the predetermined period, and a feedback control section that controls the lock-up clutch engagement pressure by way of feedback control so that the actual slip rotation is brought closer to the compensated target slip rotation.
According to another aspect of the invention, a slip control system for a torque converter employing a lock-up clutch comprises a slip-control area section that determines whether the torque converter is in a torque-converter action area or in a slip-control area according to a throttle opening and a vehicle speed, a feedforward control section that determines a lock-up clutch engagement pressure by way of feedforward control when the torque converter is shifted from the torque-converter action area to the slip-control area, a required slip rotation calculation section that calculates a required slip rotation between input and output elements of the torque converter based on engine operating conditions, a pre-compensator that determines a controlled transient characteristic of an actual slip rotation to the required slip rotation and makes a compensated target slip rotation corresponding to the controlled transient characteristic when the actual slip rotation becomes less than a predetermined slip rotation, and a feedback control section that controls the lock-up clutch engagement pressure by way of feedback control so that the actual slip rotation is brought closer to the compensated target slip rotation.